The present invention relates to a single-layer type electrophotosensitive material, which is used in image forming apparatuses such as electrostatic copying machine, facsimile and laser beam printer. More particularly, the present invention relates to a single-layer type electrophotosensitive material, which is less likely to cause wear even when used in image forming apparatuses equipped with a blade cleaning means, and is also superior in durability.
In the image forming apparatuses described above, various photosensitive materials having the sensitivity within a wavelength range of a light source used in said apparatuses have been used. One of them is an inorganic photosensitive material using an inorganic material such as selenium in a photosensitive layer, while the other one is an organic photosensitive material (OPC) using an organic material in a photosensitive layer. Among these photosensitive materials, the organic photosensitive material has widely been studied because it is easily produced as compared with the inorganic photosensitive material and has a wide range of choice of photosensitive materials such as electric charge transferring material, electric charge generating material and binder resin as well as high functional design freedom.
The organic photosensitive materials are classified roughly into a so-called multi-layer type electrophotosensitive material having a structure of an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material, which are mutually laminated, and a single-layer type photosensitive material wherein an electric charge generating material and an electric charge transferring material are dispersed in the same photosensitive layer. Among these organic photosensitive materials, it is a multi-layer type photosensitive material, which has a monopoly position in the wide market.
The single-layer type photosensitive material has become of major interest recently because of its advantages described below. That is, the single-layer type photosensitive material is superior in productivity because of its simple layer construction and can inhibit the occurrence of layer defects of the photosensitive layer, and can also improve optical characteristics because of less interface between layers. Furthermore, one photosensitive material can be used as both of positive and negative charge type photosensitive materials by using, as the electric charge transferring material, an electron transferring material and a hole transferring material in combination.
The electrophotosensitive material is used in the repeated steps of charging, exposing, developing, transferring, cleaning and charge neutralizing in the image formation process. An electrostatic latent image formed by charging/exposure is developed with a toner as a powder in the form of microparticles. Furthermore, the developed toner is transferred to a transfer material such as paper in the transfer process. However, the toner is not transferred completely (100%) and is partially remained on the photosensitive material. If the remained toner is not removed, it is made impossible to obtain a high-quality image, which is free from contamination in the repeated processes. Therefore, it is required to clean the remained toner.
In the cleaning process, a fur brush, a magnetic brush or a blade is typically used. In view of the cleaning accuracy and rationalization of apparatus construction, it is general to select a blade cleaning wherein cleaning is performed by contacting a blade-shaped resin plate directly with a photosensitive material.
As described above, according to the blade cleaning, the remained toner on the surface of the photosensitive material is removed by contacting the blade-shaped resin plate with the surface of the photosensitive material. Although the blade cleaning has high accuracy, it increases a mechanical load on the photosensitive material, thereby causing problems such as increase in wear quantity of the photosensitive layer, reduction in surface potential, lowering of the sensitivity and the like, thus making it difficult to obtain a high-quality image.
It is possible to reduce the wear quantity of the photosensitive layer by decreasing a pressing force (blade linear pressure) exerted on the surface of the photosensitive material by the cleaning blade. However, the remained toner passes through a microspace between the blade and the surface of the photosensitive material in the pressed state and adheres firmly to the surface of the photosensitive material in the state where toner particles are crushed and thus the remained toner is not removed by the blade, that is, a so-called xe2x80x9cdash markxe2x80x9d or xe2x80x9ctoner filmingxe2x80x9d phenomenon occurs to drastically reduce the potential of the surface of the photosensitive material at the portion where the toner is fused. Also no optical attenuation occurs because of light screening, thus causing defects of images.
To the contrary, when the blade linear pressure is increased to prevent dash mark or toner filming, a mechanical load on the surface of the photosensitive material increases and the wear quantity of the photosensitive layer increases, thereby deteriorating electric characteristics, thus making it difficult to obtain a high-quality image. A resonance sound is created when the blade slides over the surface of the photosensitive material, that is, a so-called xe2x80x9cblade squeakingxe2x80x9d phenomenon occurs.
An object of the present invention is to provide a single-layer type electrophotosensitive material, which exhibits good wear resistance with respect to the photosensitive layer even when used in image forming apparatuses equipped with a blade cleaning means, and is also superior in durability. Another object of the present invention is to provide a highly sensitive single-layer type electrophotosensitive material, which causes none of blade squeaking, dash mark and toner filming.
The present inventors have intensively studied and found that a single-layer type electrophotosensitive material comprising a conductive substrate and a photosensitive layer made of a binder resin containing at least an electric charge generating material and a hole transferring material and an electron transferring material as an electric charge transferring material, which is formed on the conductive substrate, wherein the binder resin contains a polycarbonate resin having a repeating structural unit represented by the general formula [1]: 
wherein R10 and R11 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and the solid content of the electric charge transferring material (hole transferring material and electron transferring material) is not less than 30% by weight and not more than 50% by weight based on the entire solid content, exhibits good wear resistance with respect to the photosensitive layer even when used in an image forming apparatus equipped with a blade cleaning means, and is also superior in durability.
Also, the present inventors have found that the single-layer type electrophotosensitive material, which further contains as the binder resin the following polycarbonate resin having a repeating structural unit represented by the general formula [2] and/or the following copolymer polycarbonate resin having a repeating structural unit represented by the general formula [3], exhibits good wear resistance with resect to the photosensitive layer even when used in an image forming apparatus equipped with a blade cleaning means, is excellent in durability, and causes none of blade squeaking, dash mark and toner filming.
A polycarbonate resin having a repeating structural unit represented by the general formula [2]: 
wherein X20, X21 and X22 are the same or different and each represents xe2x80x94(CH2)nxe2x80x94, n represents an integer of 1 to 6; R20, R21, R22 and R23 are the same or different and each represents a hydrogen atom, a phenyl group, or an alkyl or alkoxy group having 1 to 3 carbon atoms; and m represents a numerical value of 0 to 200.
In the present invention, the binder resins include a copolymer polycarbonate resin consisting of a repeating structural unit represented by the general formula [1] and a repeating structural unit represented by the general formula [2] and a mixed resin of the polycarbonate resin having a repeating structural unit represented by the general formula [1] and the polycarbonate resin having a repeating structural unit represented by the general formula [2].
A copolymer polycarbonate resin having a repeating structural unit represented by the general formula [3] 
wherein R30 and R31 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
Furthermore, the present inventors have found that each single-layer type electrophotosensitive material, which contains the following compound of the general formula [4], [5], [6] or [7] as the electron transferring material and the following compound of the general formula [8], [9], [10] or [11] as the hole transferring material, exhibits good wear resistance with respect to the photosensitive layer, causes none of blade squeaking, dash mark and toner filming, and has very high sensitivity.
A compound represented by the general formula [4]: 
wherein R40 and R41 are the same or different and each represents an alkyl group which may have a substituent.
A compound represented by the general formula [5]: 
wherein R50 and R51 are the same or different and each represents a monovalent hydrocarbon group which may have a substituent.
A compound represented by the general formula [6]: 
wherein R60 represents a halogen atom, or an alkyl or aryl group which may have a substituent; R61 represents an alkyl or aryl group which may have a substituent, or a group: xe2x80x94Oxe2x80x94R61a; and R61a represents an alkyl or aryl group which may have a substituent.
A compound represented by the general formula [7]: 
wherein R70, R71, R72 and R73 are same or different and each represents an alkyl group which may have a substituent.
A compound represented by the general formula [8]: 
wherein R80, R81, R82 and R83 are the same or different and each represents an alkyl group, an alkoxy group, an aryl group, an aralkyl group, or a halogen atom; m, n, p and q are the same or different and each represents an integer of 0 to 3; R84 and R85 are the same or different and each represents a hydrogen atom or an alkyl group; and xe2x80x94Xxe2x80x94 represents the formula: 
or the formula: 
A compound represented by the general formula [9]: 
wherein R90 and R92 are the same or different and each represents an alkyl group which may have a substituent; and R91 and R93 are different and each represents a hydrogen atom or an alkyl group which may have a substituent.
A compound represented by the general formula [10]: 
wherein R100, R101, R102, R103 and R104 are the same or different and each represents a hydrogen atom, a halogen atom, or an alkyl or alkoxy group which may have a substituent.
A compound represented by the general formula [11]: 
wherein R110, R111, R112 and R113 are the same or different and each represents a halogen atom, or an alkyl, alkoxy or aryl group which may have a substituent; and a, b, c and d are the same or different and each represents an integer of 0 to 5, provided that R110, R111, R112 and R113 may be different when a, b, c or d is 2 or more.
That is, the binder resin used in the single-layer type electrophotosensitive material of the present invention is characterized in that it contains a polycarbonate resin having a repeating structural unit represented by the general formula [1]. The repeating structural unit represented by the general formula [1] is extremely effective to improve the wear resistance of the photosensitive layer because of high molecular stiffness.
The solid content of the electric charge transferring material in the single-layer type electrophotosensitive material of the present invention is not less than 30% by weight and not more than 50% by weight based on the entire solid content. The electric charge transferring material functions like a plasticizer in the binder resin and an increase of the content reduces the strength of the photosensitive layer and deteriorates the wear resistance. Therefore, the wear resistance is improved by adjusting the solid content of the electric charge transferring material to 50% by weight or less based on the entire solid content. When the solid content of the electric charge transferring material is less than 30% by weight, the photosensitivity is lowered and the resulting single-layer type electrophotosensitive material does not have a practical sensitivity.
In case the binder resin used in the single-layer type electrophotosensitive material of the present invention contains a polycarbonate resin having a repeating structural unit represented by the general formula [1] and a repeating structural unit represented by the general formula [2], the resulting single-layer type electrophotosensitive material exhibits good wear resistance with resect to the photosensitive layer, and is also superior in durability and causes none of blade squeaking, dash mark and toner filming. Since the polycarbonate having a repeating structural unit represented by the general formula [2] has a siloxane bond in a principal chain, it reduces a friction coefficient of a cleaning blade to the surface of the photosensitive layer, and is also effective to improve the wear resistance of the photosensitive layer and prevents blade squeaking. Since the surface energy of the photosensitive layer is lowered, adhesion of the toner to the photosensitive layer, which can cause dash mark or toner filming, is less likely to occur.
When using a polycarbonate resin having repeating structural units represented by the general formulas [1] and [2], since adhesion of the toner to the surface of the photosensitive layer is less likely to occur, as described above, dash mark and toner filming are less likely to occur. It is not necessary to excessively enhance the blade linear pressure; therefore, drum squeaking and scraping of the photosensitive layer can be reduced by conditions of the image formation system.
In case the binder resin used in the single-layer type electrophotosensitive material of the present invention contains a repeating structural unit represented by the general formula [1], a repeating structural unit represented by the general formula [2] and a copolymer polycarbonate resin having a repeating structural unit represented by the general formula [3], as described above, the polycarbonate resin is effective to improve the wear resistance or surface lubricity of the photosensitive layer and the resulting photosensitive material exhibits very high sensitivity. The reason is considered as follows. That is, the polycarbonate resin having a repeating structural unit represented by the general formula [1] and the polycarbonate resin having a repeating structural unit represented by the general formula [2] are effective to improve the wear resistance or surface lubricity of the photosensitive layer, but the both are inferior in compatibility with the electric charge transferring material. To the contrary, the polycarbonate resin having a repeating structural unit represented by the general formula [3] makes it possible to improve the sensitivity because of excellent compatibility with the electric charge transferring material.
As described above, the compatibility of the binder resin with the electric charge transferring material exerts a large influence on electric characteristics. The reason is considered as follows. That is, although the electric charge transferring material is dissolved uniformly in the binder resin thus causing molecular dispersion, poor compatibility with the binder resin causes molecular agglomeration, thereby to lower the efficiency of giving and receiving of electric charges, resulting in less sensitivity. Therefore, a high sensitivity photosensitive material can be obtained by using a binder resin having good compatibility with an electric charge transferring material in combination.
Also in case the single-layer type electrophotosensitive material of the present invention contains at least one of electron transferring materials represented by the general formulas [4] to [7] and at least one of hole transferring materials represented by the general formulas [8] to [11], the resulting photosensitive material exhibits very high sensitivity.
Particularly, since the single-layer type electrophotosensitive material of the present invention contains both hole and electron transferring materials as the electric charge transferring material, a ratio of the total amount of the electric charge transferring material to the amount of the binder resin increases. Furthermore, since the electric charge generating material and the electric charge transferring material are dispersed in the form of particles in the same photosensitive layer, the single-layer type photosensitive material contains a large amount of material dispersed or dissolved in the binder resin as compared with the multi-layer type photosensitive material and the compatibility of the electric charge transferring material with the binder resin to be exerted on the sensitivity of the photosensitive material is particularly enhanced.
The electron transferring materials represented by the general formulas [4] to [7] or the hole transferring materials represented by the general formulas [8] to [11] have excellent compatibility with the binder resin (polycarbonate resin having a repeating structural unit represented by the general formula [1] or a repeating structural unit represented by the general formula [2]) used in the single-layer type electrophotosensitive material of the present invention and also exhibit large mobility and, therefore, they are extremely effective to improve the sensitivity of the photosensitive material.
Each alkyl group in the general formulas [4], [6] to [11] includes the alkyl group having 1 to 30 carbon atoms, preferably 1 to 12 carbon atoms, such as methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, t-butyl group, amyl group, or 2-ethylhexyl group.
Each alkoxy group in the general formulas [8], [10] and [11] includes the alkoxyl group having 1 to 30 carbon atoms, preferably 1 to 12 carbon atoms, such as methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group, iso-butoxy group, or t-butoxy group.
Each aryl group in the general formulas [6], [8], [11] to [14] includes the aryl group having 1 to 30 carbon atoms, preferably 1 to 16 carbon atoms, which may be substituted with alkyl group, alkoxy group or aryl group, such as phenyl group, naphthyl group, tolyl group, xylyl group, ethyl phenyl group, or biphenyl group.
Each aralkyl group in the general formulas [8] and [14] includes the aralkyl group having 7 to 30 carbon atoms, preferably 7 to 12 carbon atoms, which may be substituted with alkyl group or alkoxy group, such as benzyl group, phenethyl group or cumyl group.
The mono valent hydrocarbon group in the general formula [5] includes the alkyl group, aryl group and aralkyl group as exemplified in the general formulas [4], [6] to [11].
Each cycloalkyl group in the general formulas [12] to [14] includes the cycloalkyl group having 3 to 10 carbon atoms, preferably 3 to 8 carbon atoms, such as cyclohexyl group or cyclopentyl group.